This invention relates generally to a color electrophotographic printing machine, and more particularly concerns a chargeless electrophotographic printing machine employing a single component magnetic developer material.
In the process of electrophotographic printing, a photoconductive surface is uniformly charged and exposed to form a light image of an original document. Exposure of the charged photoconductive surface creates an electrostatic latent image corresponding to the original document. A developer mix comprising magnetic carrier granules and toner particles adhering electrostatically thereto is positioned in contact with the electrostatic latent image. The toner particles are electrostatically attracted from the carrier granules to the latent image rendering it visible. Thereafter, the toner powder image is transferred to a sheet of support material and permanently affixed thereto producing a copy of the original document. The foregoing process is described, in detail, in U.S. Pat. No. 2,297,691 issued to Carlson in 1942.
Multi-clor electrophotographic printing is substantially identical to the heretofore discussed process of black and white printing with the following distinctions. Rather than forming a total light image of the original document, the light image is filtered producing a single color light image which is a partial light image of the original document. The foregoing single color light image exposes the charged photoconductive surface to create successive single color electrostatic latent images thereon. The single color electrostatic latent images are developed with toner particles complementary in color thereto. Subsequently, successive single color powder images are transferred to a sheet of support material in superimposed registration with one another. In this manner, a multi-color powder image is formed on the sheet of support material and permanently affixed thereto forming a color copy of the original document.
Various other techniques are employed in electrophotographic printing. By way of example U.S. Pat. No. 3,563,734 issued to Shely in 1971 discloses a photoreceptor which is mounted in the form of an advanceable roll and carriage assembly. The photoreceptor is exposed to a light image of an original document and then advanced past a magnetic brush developer assembly. The magnetic brush developer assembly has magnetic, conductive particles adhering thereto. As the photoreceptor, with the charge pattern recorded thereon, advances past the magnetic brush assembly, the particles adhering thereto contact the charge pattern and are attracted thereto. These particles are then transferred to a sheet of support material secured to a transfer roll. Thereafter, the sheet of support material passes through a fusing device which permanently affixes the powder image thereto forming a black and white copy of the original document.
Other relevant patents which exemplify the foregoing type of system are U.S. Pat. Nos. 3,617,124, 3,643,629, 3,739,749 and 3,764,313. However, none of the foregoing patents appear to disclose the utilization of such a system for multi-color electrophotographic printing.
Accordingly, it is a primary object of the present invention to improve color electrophotographic printing by employing a single component developer material in conjunction with a chargeless system.